单例模式

/*单例模式：一个类中只有一个对象；步骤：1.构造函数私有（控制别的程序不能创建对象）2.创建一个对象3.提供方法给外界访问*/// 饿汉式/*Single 类class  Single{private int num;public void  setNum(int num){this.num=num;}public int getNum(){return num;}private Single(){}    staticSingle s=new Single();    public static Single getInstance(){return s;}}*///懒汉式class Single{private int num;public void  setNum(int num){this.num=num;}public int getNum(){return num;}static Single s=null;private Single(){}    public static Single getInstance(){if(s==null){synchronized (Single.class){if(s==null)s=new Single();}}return s;}}//测试功能class SingleDemo{public static void main(String[] args){Single ss=Single.getInstance();Single sss=Single.getInstance();ss.setNum(30);System.out.println(sss.getNum());}}